The present invention relates to a method for producing a minute particle or a quantum thin line constructed of a metal or semiconductor that is minute enough to cause a quantum size effect on an insulating substrate or a semiconductor substrate via an insulating layer and to a semiconductor device that employs a quantum thin line utilized as a single electron device or a quantum effect device.
The large-scale integrated circuits (LSIs) that have supported the development of electronics and currently become the industrial nucleus have made great strides in terms of their performances toward larger capacity, higher speed, lower consumption of power and so on through the microstructural progress thereof. However, it is considered that the conventional device reaches the limit in terms of the principle of operation when the device size becomes 0.1 xcexcm or smaller, and accordingly, there are conducted energetic researches on a new device based on a new principle of operation. As to this new device, there is a device having a microstructure called the nanometer-size quantum dot or quantum thin line. The nanometer-size quantum dot is energetically examined together with a variety of quantum effect devices, particularly for the application thereof to a single electron device utilizing the Coulomb blockade phenomenon. The nanometer-size quantum thin line is expected to be applied to a super-high-speed transistor utilizing the quantum effect.
Particularly, in regard to the quantum thin line, there is carried out trial production of a semiconductor quantum device based on a new principle of operation that the degree of freedom of an electron is limited by confining the electron in a semiconductor layer having a width approximately equal to that of the electron wavelength (de Broglie wavelength) in a semiconductor crystal and a quantization phenomenon caused by this is utilized. The wavelength of an electron in a semiconductor layer is about 10 nm. Therefore, it is theoretically derived that, if an electron is confined in a semiconductor thin line (quantum thin line) having a width of about 10 nm, then the electron can move in this thin line while being scarcely scattered, for the achievement of the increased mobility of the electron. By forming a conductive layer in which a number of quantum thin lines as described above are arranged in a plane and controlling the number of electrons inside this layer by the operation of a gate electrode, there can be produced a quantum thin line transistor having a higher operating speed than that of the conventional transistor. By incorporating a number of the above quantum thin lines into a laser light emitting layer, there can be obtained a semiconductor laser device that has a sharp spectrum, high-efficiency and excellent high-frequency characteristics even with a small injection current.
Conventionally, as a method for forming a quantum thin line, there have been proposed methods as disclosed in the following reference documents (1) and (2).
(1) Japanese Patent Laid-Open Publication No. HEI 5-29632
FIGS. 15A through 15F are process charts showing the xe2x80x9cMethod for producing silicon quantum thin line on silicon substrate utilizing anisotropic etchingxe2x80x9d disclosed in the above reference document (1).
First, as shown in FIG. 15A, an etching mask 112 made from a silicon oxide film or a silicon nitride film is formed on a silicon (100)-substrate 111. Next, as shown in FIG. 15B, the silicon (100)-substrate is etched by using a silicon anisotropic etching liquid of potassium hydroxide water and so on having an etching rate characteristic that largely varies depending on the orientation of silicon. Since the etching rate of the (111) plane is slower than the etching rate of the (110) plane and (100) plane by about two orders of magnitude, a projecting portion having a triangular cross-section shape is formed on the surface of the silicon (100)-substrate 111 after etching.
Next, as shown in FIG. 15C, after the removal of the etching mask 112 (shown in FIG. 15B), a silicon nitride film 113 that becomes an oxidation-resistant mask layer is formed, and thereafter a resist pattern 114 is formed so as to cover at least the top of the projecting portion having a triangular cross-section shape.
Next, as shown in FIG. 15D, the silicon nitride film 113 is etched using a resist 114 as a mask, and further the silicon (100)-substrate 111 is subjected to isotropic etching.
Next, as shown in FIG. 15E, after the removal of the resist 114 (shown in FIG. 15D), the silicon (100)-substrate 111 is oxidized to form an oxide film 116. In this stage, the silicon nitride film 113 serves as the oxidation-resistant mask, and therefore, a portion in the vicinity (indicated by the reference numeral 115 in FIG. 15E) of the top of the projecting portion having a triangular cross-section shape is not oxidized.
Finally, as shown in FIG. 15F, if the silicon nitride film 113 (shown in FIG. 15E) is removed, then a silicon thin line 115 that is insulated and isolated from the silicon (100)-substrate 111 by the oxide film 116 is formed at the top of the projecting portion having a triangular cross-section shape.
(2) Japanese Patent Laid-Open Publication No. HEI 8-288499
FIGS. 16A through 16G are process charts showing the xe2x80x9cQuantum thin line forming method utilizing sticking of two silicon wafers and etching mask composed of aside wallxe2x80x9d disclosed in the above reference document (2).
First, as shown in FIG. 16A, a projecting portion 122 having a thickness of about 10 nm is formed on a silicon substrate 121 by dry etching.
Subsequently, as shown in FIG. 16B, a SiOx-based insulating film 123 is formed so as to flatten the entire substrate.
Next, as shown in FIG. 16C, the substrate is inverted from the state shown in FIG. 16B and stuck on another silicon substrate 124 with the surface of the SiOx-based insulating film 123 put in contact with the silicon substrate 124.
Next, as shown in FIG. 16D, the silicon substrate 121 (shown in FIG. 16C) is abraded by the CMP (Chemical Mechanical Polishing) method until the SiOx-based insulating film 123 is exposed. In this case, an island-shaped silicon layer 125 is left as buried in the SiOx-based insulating film 123.
Next, by forming a polysilicon layer including an impurity to a thickness of about 10 nm by the thermal CVD (Chemical Vapor Deposition) method and thereafter performing anisotropic etching via a resist mask, there is formed a polysilicon pattern 126 where the processed end surface is positioned in the vicinity of the center of the island-shaped silicon layer 125.
Next, as shown in FIG. 16E, a thermo-oxidized film 127 having a film thickness of 1 to 10 nm is formed on the exposed portion of the island-shaped silicon layer 125 and the polysilicon pattern 126 through a thermo-oxidizing process.
Next, as shown in FIG. 16F, a side wall 128 is formed on the processed end surface of the polysilicon pattern 126 by etchback.
Next, as shown in FIG. 16G, wet processing is performed on condition that a selection ratio relative to the island-shaped silicon 125 can be assured, consequently removing the polysilicon pattern 126 (shown in FIG. 16F). Subsequently, the island-shaped silicon 125 (shown in FIG. 16F) is etched on condition that the selection ratio relative to a SiOx side wall 128 can be assured, consequently forming a quantum thin line 129.
The aforementioned prior art techniques (1) and (2) have the problems as follows.
(1) According to the xe2x80x9cMethod for producing silicon quantum thin line on silicon substrate utilizing anisotropic etchingxe2x80x9d of the aforementioned reference document of Japanese Patent Laid-Open Publication No. HEI 5-29632, the silicon thin line is formed at the top of the silicon substrate having a triangular cross-section shape. Therefore, the surface flatness of the silicon substrate becomes degraded as a consequence of an increase in size of the stepped portion on the silicon substrate. This results in a difficulty in forming a single-electron transistor.
(2) According to the xe2x80x9cQuantum thin line forming method utilizing sticking of two silicon wafers and etching mask composed of side wallxe2x80x9d of the aforementioned reference document of Japanese Patent Laid-Open Publication No. HEI 8-288499, there are needed two silicon substrates as well as the special substrate forming technique of sticking two silicon substrates on each other via an insulating layer. The height of the quantum thin line is determined depending on the dry etching depth of the silicon substrate via the resist mask, and it is difficult to control the dry etching depth in nanometer size in the above case.
Accordingly, the object of the present invention is to provide a quantum thin line producing method capable of easily forming a single electron transistor that employs a quantum thin line and has good surface flatness of the silicon surface obtained through quantum thin line formation and of forming a quantum thin line having a complete electron confining region with good controllability using one semiconductor substrate of a silicon substrate, a GaAs substrate or the like without using any special substrate forming technique as well as a semiconductor device employing the quantum thin line.
In order to achieve the aforementioned object, according to the first aspect of the present invention, there is provided a quantum thin line producing method comprising the steps of:
forming a stepped portion on a semiconductor substrate;
forming a nitride film on an upper portion and a lower portion of the semiconductor substrate by which the stepped portion is formed;
masking a region of the nitride film which covers the lower portion of the semiconductor substrate and etching back the nitride film, consequently exposing the upper portion of the semiconductor substrate;
forming a first oxide film by oxidizing the exposed upper portion of the semiconductor substrate and forming a linear protruding portion on the semiconductor substrate along a side surface of the nitride film;
partially etching the first oxide film located on the protruding portion of the semiconductor substrate, consequently exposing a tip of the protruding portion;
epitaxially growing a thin line portion on an exposed region of the tip of the protruding portion of the semiconductor substrate;
removing the nitride film and the first oxide film after the epitaxial growth of the thin line portion; and
forming a quantum thin line isolated from the semiconductor substrate by a second oxide film formed by oxidizing the semiconductor substrate after the removal of the nitride film and the first oxide film.
According to the quantum thin line producing method of the present invention, the linear protruding portion can be formed on the semiconductor substrate by means of the general film forming technique, lithographic technique and etching technique, and the exposed region can be formed at the tip of the protruding portion. This enables the positional control of the quantum thin line and the formation of the quantum thin line on a relatively flat semiconductor substrate. Therefore, a single electron transistor can be easily formed. Since no special fine processing technique is used, there can be provided a quantum thin line producing method of a high yield and high productivity appropriate for mass production at reduced producing cost.
According to the second aspect of the present invention, there is provided a quantum thin line producing method comprising the steps of:
forming a stepped portion on a semiconductor substrate;
forming a first nitride film on an upper portion and a lower portion of the semiconductor substrate by which the stepped portion is formed;
masking a region of the first nitride film which covers the lower portion of the semiconductor substrate and etching back the first nitride film, consequently exposing the upper portion of the semiconductor substrate;
forming a second nitride film on the exposed upper portion of the semiconductor substrate and the first nitride film and then performing etching back, consequently exposing the upper portion of the semiconductor substrate;
forming a first oxide film by oxidizing the exposed upper portion of the semiconductor substrate and forming a linear protruding portion on the semiconductor substrate along a side surface of the first nitride film;
partially etching the first oxide film located on the protruding portion of the semiconductor substrate, consequently exposing a tip of the protruding portion;
epitaxially growing a thin line portion on an exposed region located at a tip of the protruding portion of the semiconductor substrate;
removing the first and second nitride films and the first oxide film after the epitaxial growth of the thin line portion; and
forming a quantum thin line isolated from the semiconductor substrate by a second oxide film formed by oxidizing the semiconductor substrate after the removal of the first and second nitride films and the first oxide film.
According to the above quantum thin line producing method, the linear protruding portion can be formed on the semiconductor substrate by means of the general film forming technique, lithographic technique and etching technique, and the exposed region can be formed at the tip of the protruding portion. This enables the positional control of the quantum thin line and the formation of the quantum thin line on a relatively flat semiconductor substrate. Therefore, a single electron transistor can be easily formed. Since no special fine processing technique is used, there can be provided a quantum thin line producing method of a high yield and high productivity appropriate for mass production at reduced producing cost. Furthermore, the formation and etchback of the second nitride film are performed after the dry etching of the first nitride film, and therefore, the positional control margin of the photoresist during the etching of the first nitride film can be approximately doubled.
According to the third aspect of the present invention, there is provided a quantum thin line producing method comprising the steps of:
forming a groove having a rectangular cross-section shape on a semiconductor substrate;
forming a nitride film on the semiconductor substrate on which the groove is formed;
etching back the nitride film, consequently exposing both side portions of the semiconductor substrate located on both sides of the groove;
forming a first oxide film by oxidizing the exposed region of the semiconductor substrate located on both sides of the groove and forming linear protruding portions on the semiconductor substrate along both side surfaces of the first nitride film;
partially etching the first oxide film located on both protruding portions of the semiconductor substrate, consequently exposing tips of both the protruding portions;
epitaxially growing thin line portions on exposed portions located at the tips of both the protruding portions of the semiconductor substrate;
removing the nitride film and the first oxide film after the epitaxial growth of the thin line portions; and
forming quantum thin lines isolated from the semiconductor substrate by a second oxide film formed by oxidizing the semiconductor substrate after the removal of the nitride film and the first oxide film.
According to the above quantum thin line producing method, the linear protruding portion can be formed on the semiconductor substrate by means of the general film forming technique, lithographic technique and etching technique, and the exposed region can be formed at the tip of the protruding portion. This enables the positional control of the quantum thin line and the formation of the quantum thin line on a relatively flat semiconductor substrate. Therefore, a single electron transistor can be easily formed. Since no special fine processing technique is used, there can be provided a quantum thin line producing method of a high yield and high productivity appropriate for mass production at reduced producing cost. Furthermore, there can be eliminated the process for forming a resist in the region above the groove portion of the nitride film before the etchback of the nitride film and forming a mask.
According to one embodiment, the step for epitaxially growing the thin line portion in the exposed region located at the tip of the protruding portion of the semiconductor substrate comprises: introducing the semiconductor substrate into a reaction chamber and discharging air inside the reaction chamber so that the reaction chamber comes to have a high vacuum of not higher than 10xe2x88x926 Torr; and thereafter flowing a material gas into the reaction chamber so as to perform vapor growth of the thin line portion under a material gas partial pressure of not higher than 10xe2x88x922 Torr.
According to the quantum thin line producing method of the above embodiment, after introducing the semiconductor substrate into the reaction chamber and the atmospheric components and the impurities of moisture component and the like are discharged so that the reaction chamber comes to once have a high vacuum of not higher than 106 Torr, allowing the epitaxial growth in the highly clean environment to be promoted. Thereafter, by flowing a material gas and setting the material gas partial pressure to 10xe2x88x922 Torr or lower, vapor growth is performed only in the exposed region at the tip or top of the semiconductor substrate where the thin line portion grows. If the material gas partial pressure exceeds 10xe2x88x922 Torr in this stage of reaction, then the film growth rapidly starts on the entire surface of the insulating thin film, failing in achieving selective growth. Therefore, by controlling the degree of vacuum inside the reaction chamber, the amount of material gas to be introduced, the time of introduction, the substrate temperature and so on by means of a general high-vacuum CVD apparatus, the quantum thin line of the desired size is formed with high reproducibility.
In one embodiment, the quantum thin line is made of silicon and,
any one of monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8), dichlorosilane (SiH2Cl2) and tetrachlorosilane (SiCl4) is used as a material gas.
According to the quantum thin line producing method of the above embodiment, a quantum thin line made of silicon can be formed only in the exposed region located at the tip of the protruding portion of the semiconductor substrate by using any one of monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8), dichlorosilane (SiH2Cl2) and tetrachlorosilane (SiCl4) as a material gas and causing reaction by means of the general CVD apparatus.
In one embodiment, the quantum thin line is made of germanium and,
any one of monogermane (GeH4), digermane (Ge2H6) and germanium tetrafluoride (GeF4) is used as a material gas.
According to the quantum thin line producing method of the above embodiment, a quantum thin line made of germanium can be formed only in the exposed region located at the tip of the protruding portion of the semiconductor substrate by using any one of monogermane (GeH4), digermane (Ge2H6) and germanium tetrafluoride (GeF4) as a material gas and causing reaction by means of the general CVD apparatus.
In one embodiment, the quantum thin line is made of silicon germanium and,
a mixed gas comprised of a gas of any one of monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8), dichlorosilane (SiH2Cl2) and tetrachlorosilane (SiCl4) and a gas of any one of monogermane (GeH4), digermane (Ge2H6) and germanium tetrafluoride (GeF4) is used as a material gas.
According to the quantum thin line producing method of the above embodiment, a quantum thin line made of silicon germanium can be formed only in the exposed region located at the tip of the protruding portion of the semiconductor substrate by using a mixed gas comprised of a gas of any one of monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8), dichlorosilane (SiH2Cl2) and tetrachlorosilane (SiCl4) and a gas of any one of monogermane (GeH4), digermane (Ge2H6) and germanium tetrafluoride (GeF4) as a material gas and causing reaction by means of the general CVD apparatus.
In one embodiment, the quantum thin line is made of aluminum and,
an organic aluminum is used as a material.
According to the quantum thin line producing method of the above embodiment, the quantum thin line made of aluminum can be formed only in the exposed region located at the tip of the protruding portion of the semiconductor substrate by using an organic aluminum of dimethyl aluminum hydride (DMAH: (CH3)2AlH) or the like as a material and causing reaction by means of the general CVD apparatus.
One embodiment provides a semiconductor device having a source region, a drain region, a channel region located between the source region and the drain region, a gate region for controlling a channel current flowing through the channel region, a floating gate region located between the channel region and the gate region, a first insulating film located between the floating gate region and the gate region and a second insulating film located between the channel region and the floating gate region,
the floating gate region being comprised of a quantum thin line formed by the quantum thin line producing method.
According to the semiconductor device employing the quantum thin line of the above embodiment, the quantum thin line made of a semiconductor (or metal) formed by the above quantum thin line producing method is made to serve as the floating gate region. With this arrangement, the electric charge accumulation is reduced, and the amount of electric charges to be injected into the floating gate region can be reduced. This enables the obtainment of a non-volatile memory of a small consumption of power, a high density and a large capacity. A non-volatile memory of a high yield and high productivity appropriate for mass production can be obtained at low cost. Furthermore, the semiconductor device employing the quantum thin line of the embodiment can be mounted on the same substrate as that of a silicon-based large-scale integrated circuit as a semiconductor device having a quantum thin line that becomes the basis of a single electron device.
One embodiment provides a semiconductor device having a source region, a drain region, a channel region located between the source region and the drain region, a gate region for controlling a channel current flowing through the channel region and a gate insulating film located between the channel region and the gate region,
the channel region being comprised of a quantum thin line formed by the quantum thin line producing method.
According to the semiconductor device employing the quantum thin line of the above embodiment, the quantum thin line made of a semiconductor (or metal) formed by the above quantum thin line producing method is made to serve as the channel region. With this arrangement, the channel region is quantized in the direction perpendicular to the lengthwise direction of the quantum thin line, exhibiting linear conduction. This enables the obtainment of a transistor that can operate at a super high speed and the provision of a low-cost super-high-speed transistor of a high yield and high productivity appropriate for mass production. The semiconductor device employing the quantum thin line of the embodiment can be mounted on the same substrate as that of a silicon-based large-scale integrated circuit serving as a semiconductor device having a quantum thin line that becomes the basis of a quantum effect device.
One embodiment provides a semiconductor device comprising: a quantum thin line formed by the quantum thin line producing method; an insulating film formed with interposition of the quantum thin line; and electrodes formed to sandwich the insulating film, wherein
the quantum thin line emits light when a voltage is applied across the electrodes.
According to the semiconductor device employing the quantum thin line of the above embodiment, by virtue of the quantum confining effect obtained by interposing the quantum thin line formed by the aforementioned quantum thin line producing method between the insulating film portions and further interposing the insulating film portions between the electrodes, the quantum thin line comes to have a direct transition type band structure. If a voltage is applied across the electrodes to flow a tunnel current for the injection of electrons into the quantum thin line, then electron transition occurs in the quantum thin line, causing light emission. Therefore, a light-emitting device of a high yield and high productivity appropriate for mass production can be provided at low cost. Furthermore, the semiconductor device employing the quantum thin line of the embodiment can be mounted on the same substrate as that of a silicon-based large-scale integrated circuit as a semiconductor device having a quantum thin line that becomes the basis of a quantum effect device or a single electron device. By applying this semiconductor device to a light-emitting device or a photoelectric transducing device, an electronic circuit and an optical communication circuit can be combined with each other.
One embodiment provides a semiconductor device provided with a quantum thin line which is formed by the quantum thin line producing method and of which one portion is an n-type semiconductor and the other portion is a p-type semiconductor, wherein
the quantum thin line emits light when a voltage is applied across the n-type semiconductor portion and the p-type semiconductor portion of the quantum thin line.
According to the semiconductor device employing the quantum thin line of the above embodiment, one portion of the quantum thin line formed by the aforementioned quantum thin line producing method is constructed of the n-type semiconductor and the other portion of the quantum thin line is constructed of the p-type semiconductor. The quantum thin line has a direct transition type band structure by virtue of the quantum confining effect, and a pn junction is formed in the boundary region located between the n-type semiconductor and the p-type semiconductor of the quantum thin line. Therefore, by applying a voltage across the n-type semiconductor and the p-type semiconductor, reunion of an electron with a hole occurs in the pn junction portion, causing light emission. Therefore, a light-emitting device of a high yield and high productivity appropriate for mass production can be provided at low cost. Furthermore, the semiconductor device employing the quantum thin line of the embodiment can be mounted on the same substrate as that of a silicon-based large-scale integrated circuit as a semiconductor device having a quantum thin line that becomes the basis of a quantum effect device or a single electron device. By applying this semiconductor device to a light-emitting device or a photoelectric transducing device, an electronic circuit and an optical communication circuit can be combined with each other.
One embodiment provides a semiconductor device provided with three or more quantum thin lines formed roughly parallel to one another at set intervals by the quantum thin line producing method, wherein
a semiconductor forbidden bandwidth of any one of the three or more quantum thin lines, the one quantum thin line being located inside, is made smaller than an energy gap of the forbidden bandwidth of the quantum thin lines located on both sides of the one quantum thin line, and wherein
the quantum thin line located inside the quantum thin lines located on both sides emits light when a voltage is applied across the quantum thin lines located on both sides.
According to the semiconductor device employing the quantum thin line of the above embodiment, the semiconductor forbidden bandwidth of any one of the three or more quantum thin lines formed by the aforementioned quantum thin line producing method, the one quantum thin line being located inside, is made smaller than the energy gap of the forbidden bandwidth of the quantum thin lines located on both sides of the one quantum thin line. The quantum thin line comes to have the direct transition type band structure by virtue of the quantum confining effect and also the double hetero structure in which the efficiency of reunion of an electron with a hole is high. Therefore, by applying a voltage across the quantum thin lines located on both sides, the reunion of an electron with a hole occurs in the quantum thin line which is located inside and the energy gap of the forbidden bandwidth of which is small, causing light emission. Therefore, a light-emitting device of a high yield and high productivity appropriate for mass production can be provided at low cost. Furthermore, the semiconductor device employing the quantum thin line of the embodiment can be mounted on the same substrate as that of a silicon-based large-scale integrated circuit as a semiconductor device having a quantum thin line that becomes the basis of a quantum effect device or a single electron device. By applying this semiconductor device to a light-emitting device or a photoelectric transducing device, an electronic circuit and an optical communication circuit can be combined with each other.